Proton Aurora on Mars: A Dayside Phenomenon Pervasive in Southern Summer

We present observations of proton aurora at Mars made using the Imaging UltraViolet Spectrograph (IUVS) onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Martian proton aurora display a prominent intensity enhancement in the hydrogen Lyman‐alpha (121.6 nm) emission between ~110 and 150 km altitude. Using altitude‐intensity profiles from periapsis limb scan data spanning nearly two Martian years, we create a comprehensive database of proton aurora and characterize their phenomenology. Due to Mars\u27 lack of a global dipole magnetic field, Martian proton aurora are expected to form on the dayside via electron stripping and charge exchange between solar wind protons and the neutral corona. We observe proton aurora in ~14% of dayside periapsis profiles (with notable seasonal variability), making proton aurora the most commonly observed type of aurora at Mars. We determine that the primary factors influencing proton aurora occurrence rates are solar zenith angle and season. The highest proton aurora occurrence rates are at low solar zenith angles on the Mars dayside, consistent with known formation processes. Proton aurora have highest emission enhancements, peak intensities, peak altitudes, and occurrence rates (nearing 100%) around southern summer solstice. This time period corresponds with the seasonal inflation of the neutral lower atmosphere, the onset of Martian dust storm season, seasonally increased coronal hydrogen column densities, and higher atmospheric temperature and solar wind flux following perihelion. The results of our study provide a new understanding of the primary factors influencing proton aurora, and the long‐term variability of these phenomena as observed over multiple Mars years

Advancing Our Understanding of Martian Proton Aurora through a Coordinated Multi-Model Comparison Campaign

Proton aurora are the most commonly observed yet least studied type of aurora at Mars. In order to better understand the physics and driving processes of Martian proton aurora, we undertake a multi-model comparison campaign. We compare results from four different proton/hydrogen precipitation models with unique abilities to represent Martian proton aurora: Jolitz model (3-D Monte Carlo), Kallio model (3-D Monte Carlo), Bisikalo/Shematovich et al. model (1-D kinetic Monte Carlo), and Gronoff et al. model (1-D kinetic). This campaign is divided into two steps: an inter-model comparison and a data-model comparison. The inter-model comparison entails modeling five different representative cases using similar constraints in order to better understand the capabilities and limitations of each of the models. Through this step we find that the two primary variables affecting proton aurora are the incident solar wind particle flux and velocity. In the data-model comparison, we assess the robustness of each model based on its ability to reproduce a MAVEN/IUVS proton aurora observation. All models are able to effectively simulate the data. Variations in modeled intensity and peak altitude can be attributed to differences in model capabilities/solving techniques and input assumptions (e.g., cross sections, 3-D versus 1-D solvers, and implementation of the relevant physics and processes). The good match between the observations and multiple models gives a measure of confidence that the appropriate physical processes and their associated parameters have been correctly identified and provides insight into the key physics that should be incorporated in future models

Fabry-Perot Observations of the Hydrogen Geocorona

Within the framework of this dissertation, the Fabry-Perot annular summing optical system was completely redesigned and constructed in order to minimize vignetting and to facilitate improved intensity, wavelength, and linewidth calibration for the study of geocoronal Balmer α. A signal to noise ratio of approximately 50 was obtained for a typical geocoronal Balmer α intensity in a ten minute integration, covering a 75 km/s velocity interval with 3.75 km/s velocity resolution, from a 1.5° beam on the sky.This newly designed Fabry-Perot annular summing spectrometer was operated for two years (2000–2001) at the University of Wisconsin\u27s Pine Bluff Observatory (PBO). An extensive geocoronal Balmer α data set of approximately 1500 spectra over 71 nights was obtained; this represents the highest quality geocoronal Balmer α line profile data set to date.This dissertation reviews past geocoronal observations, the atomic physics associated with geocoronal Balmer α emission, and Fabry-Perot annular summing spectroscopy. The design, calibration, and performance of the PBO Fabry-Perot are discussed at length. The full 2000–2001 PBO geocoronal Balmer α data set is presented including: Balmer α intensities, Doppler widths, and data regarding cascade contributions to the emission. A diurnal signal is clearly observed in the line intensity, but not in the line width. A significant decrease in Balmer α Doppler width with increasing shadow altitude was detected every night in which a wide range of shadow altitudes was observable. Cascade contributions to the Balmer α emission were found to be approximately 5%, consistent with recent estimates. Preliminary applications of the nonisothermal radiative transport code lyao_rt to a subset of the PBO data indicates good general agreement both with regard to trends in the emission line intensity and to line width, indicating that a new level of understanding of the geocorona is likely to emerge through forward-modeling analysis

A Systematic Program for Ground-Based Fabry-Perot Observations of the Neutral Hydrogen Exosphere

Large gains in the sensitivity of Fabry-Perots for geocoronal research have been achieved at the University of Wisconsin employing the technique of CCD annular summing spectroscopy. Earlier \u27demonstration observations\u27 of this technique lead to a significant new understanding of geocoronal hydrogen excitation. This paper will outline a new ground-based observing program which is building on these earlier observations in order to obtain definitive data regarding the physical processes which govern the abundance and transport of atomic hydrogen in the earth\u27s atmosphere. Two double-etalon Fabry-Perot spectrometers have been installed at the University of Wisconsin\u27s Pine Bluff Observatory (WI) for the purpose of making a systematic series of high spectral resolution (R approximately equals 100,000) line profile, and intensity observations of geocoronal hydrogen nightglow. For the first time it will be possible to obtain coincident observations of geocoronal hydrogen Balmer-alpha and Balmer- beta with sufficient signal-to-noise for detailed line profile studies. Because the geocoronal Balmer-beta emission is about one tenth the intensity of Balmer-alpha, the fitness of this line has frustrated past attempts to determine its profile; however, gains in sensitivity afforded by the annular-summing technique make these new observations possible. It is anticipated that these simultaneous observations will provide a means by which to isolate previously observed perturbations to the Balmer-alpha line, the components of which may arise from both contributions due to quantum mechanical fine structure and the non-Maxwellian dynamics of the hydrogen exosphere. Each of these instruments employs the annular summing technique in which the Fabry-Perot\u27s annular fringe pattern is imaged onto a low noise CCD chip. Using the property that equal area annuli correspond to equal spectral intervals, software is used to divide the CCD image into equal area annular bins, whereby the Fabry-Perot interference pattern is converted into a useful spectral profile. This paper will describe the instrumentation, and how it relates to the planned observational program

New Analysis of the Deep Impact Comet 9P/Tempel 1 Event Using High Resolution Spectroscopy: Evidence From 630 NM [O( 1 D)] Emission

Thorough analysis of narrow bandpass high spectral resolution (R ≈ 100,000) observations of [O 1 D] 630nm emission from comet 9P/Tempel 1 taken over a ~1’ FOV both before and after the Deep Impact event provides evidence for a long-lived high velocity jet-like feature. The observations were obtained with an all-reflective spatial heterodyne spectrometer (SHS) coupled to the McMath-Pierce Main telescope. Several spectra centered on Tempel 1 were acquired during the period of 07/04/2005-07/06/2005 UT. We report here on the presence and evolution of a cometary emission feature that appears consistently and exclusively in the post-impact narrow-band spectra centered near the telluric [O 1 D] 630nm emission line. This cometary emission feature shows substantial and distinct Doppler shifts over consecutive post-impact observational nights and if the feature isthe anticipated [O 1 D], the corresponding line of sight velocities are -13.4 to -6.5 km/s, relative to the comet’s rest frame

Line Profile Measurements of the Lunar Exospheric Sodium

We report ongoing results of a program to measure the lunar sodium exospheric line profile from near the lunar limb out to two lunar radii (approx 3500 km). These observations are conducted from the National Solar Observatory McMath-Pierce telescope using a dual-etalon Fabry-Perot spectrometer with a resolving power of 180,600 (1.7 km/s) to measure line widths and velocity shifts of the Na D2 (5889 950 A) emission line in equatorial and polar regions at different lunar phases. The typical field of view (FOV) is 3 arcmin (approx 360 km) with an occasional smaller 1 arcmin FOV used right at the limb edge. The first data were obtained from full Moon to 3 days following full Moon (waning phase) in March 2009 as part of a demonstration run aimed at establishing techniques for a thorough study of temperatures and velocity variations in the lunar sodium exosphere. These data indicate velocity displacements from different locations off the lunar limb range between 150 and 600 m/s from the lunar rest velocity with a precision of +/- 20 to +/- 50 m/s depending on brightness. The measured Doppler line widths for observations within 10.5 arcmin of the east and south lunar limbs for observations between 5 deg and 40 deg lunar phase imply temperatures ranging decreasing from 3250 +/- 260K to 1175 +/- 150K. Additional data is now being collected on a quarterly basis since March 2011 and preliminary results will be reported

A Near-UV Spatial Heterodyne Spectrometer for Interstellar [OII] Emission Line Studies

Using a newly developed spatial heterodyne spectrometer, we have obtained the first radial velocity resolved observations of interstellar 3727 A emission and confirmed the superb performance of the technique for observing spatially extended faint sources. From the publisher\u27s website

Geocoronal Fine-Structure Cascade Excitation Constraints for Ground-Based Observations and Modeling

Night-time Geocoronal hydrogen Balmer-alpha emission line-shapes, obtained by Fabry-Perot at Pine Bluff, WI, indicate a decrease in cascade contribution to the total Balmer-alpha observed intensity with viewing geometry (shadow altitude). Accurately accounting for cascade’s redwing line-shape contribution is critical to interpreting individual line-shape observations for residual exospheric dynamic signatures. Poor cascade (or Galactic background) model fits can mask sought after dynamics, leading to misinterpretation of the Balmer-alpha line profile, and erroneously high effective exospheric temperatures retrieved from the data-model fits.Roesler et al. (2014) showed relative cascade contributions to Balmer-alpha profiles could be determined with near simultaneous Balmer-beta observations (i.e., by Balmer-beta/Balmer-alpha line ratio). Roesler et al. (2014) also noted that, due to multiple scattering differences in geocoronal hydrogen for Lyman-beta and Lyman-gamma (responsible for Balmer-alpha and Balmer-beta respectively), there is a trend for the cascade to become a smaller fraction of the Balmer-alpha intensity at larger shadow altitudes.We have used near coincident Balmer-alpha and Balmer-beta data, obtained from the Wisconsin H-alpha Mapper (WHAM) Fabry-Perot, to parameterize the cascade contribution to the Balmer-alpha line profile as a function of shadow altitude. This result is in good agreement with direct cascade determinations from time-averaged Balmer-alpha line profile data, obtained by high resolution Fabry-Perot at Pine Bluff, WI. We will discuss the sensitivity of this line ratio to solar Lyman flux, and how it could be used to constrain the underlying Geocoronal hydrogen distribution

First Performance Results of a New Geocoronal Balmer-Alpha Field-Widened Spatial Heterodyne Spectrometer

During 2013, a new, high resolution field-widened spatial heterodyne spectrometer (FW-SHS) uniquely designed to observe geocoronal Balmer-alpha emission ([Ha], 6563A) was installed at Pine Bluff Observatory (PBO) near Madison Wisconsin. FW-SHS observations were compared with an already well-characterized dual-etalon Fabry Perot Interferometer (FPI) optimized for [Ha], also at PBO. The FW-SHS is a robust new Fourier-transform instrument that combines a large throughput advantage with high spectral resolution and a relatively long spectral baseline (~10x that of the FPI) in a compact, versatile instrument with no moving parts. Coincident [Ha] observations by FW-SHS and FPI were obtained over similar integration times, resolving power (~80,000 at [Ha]) and field-of-view (1.8 and 1.4 degrees, respectively). This paper describes the FW-SHS first light performance and [Ha] observational results collected from observing nights across 2013 and 2014. Initial FW-SHS observations of Balmer-alpha intensity and temperature (doppler width) vs. viewing geometry (shadow altitude) show excellent relative agreement with the geocoronal observations previously obtained at PBO by FPI. The FW-SHS is capable of determining geocoronal Balmer-alpha doppler shifts on the order of 100 m/s across a 640km/s [Ha] spectral bandpass,with a temporal resolution on the order of minutes. These characteristics make the FW-SHS well suited for spectroscopic studies of relatively faint, diffuse-source geocoronal Balmer-alpha emission from Earths upper atmosphere (~2-14R) and the interstellar medium in our Galaxy. Current and future observations expand long-term geocoronal hydrogen observation data sets already spanning two solar maximums

OH Absorption Spectroscopy in a Flame Using Spatial Heterodyne Spectroscopy

We demonstrate measurements of OH absorption spectra in the post-flame zone of a McKenna burner using spatial heterodyne spectroscopy (SHS). SHS permits high-resolution, high-throughput measurements. In this case the spectra span ∼308–310 nm with a resolution of 0.03 nm, even though an extended source (extent of ∼2×10−7 m2 rad2) was used. The high spectral resolution is important for interpreting spectra when multiple absorbers are present for inferring accurate gas temperatures from measured spectra and for monitoring weak absorbers. The present measurement paves the way for absorption spectroscopy by SHS in practical combustion devices, such as reciprocating and gas-turbine engines